libgsm/preprocess.c

   1 /*
   2  * Copyright 1992 by Jutta Degener and Carsten Bormann, Technische
   3  * Universitaet Berlin.  See the accompanying file "COPYRIGHT" for
   4  * details.  THERE IS ABSOLUTELY NO WARRANTY FOR THIS SOFTWARE.
   5  */
   6
   7 /* $Header: /cvsroot/sox/sox/libgsm/preprocess.c,v 1.1 2007/09/06 16:50:55 cbagwell Exp $ */
   8
   9 #include        <stdio.h>
  10 #include        <assert.h>
  11
  12 #include "private.h"
  13
  14 #include        "gsm.h"
  15
  16 /*      4.2.0 .. 4.2.3  PREPROCESSING SECTION
  17  *
  18  *      After A-law to linear conversion (or directly from the
  19  *      Ato D converter) the following scaling is assumed for
  20  *      input to the RPE-LTP algorithm:
  21  *
  22  *      in:  0.1.....................12
  23  *           S.v.v.v.v.v.v.v.v.v.v.v.v.*.*.*
  24  *
  25  *      Where S is the sign bit, v a valid bit, and * a "don't care" bit.
  26  *      The original signal is called sop[..]
  27  *
  28  *      out:   0.1................... 12
  29  *           S.S.v.v.v.v.v.v.v.v.v.v.v.v.0.0
  30  */
  31
  32
  33 void Gsm_Preprocess (
  34         struct gsm_state * S,
  35         word             * s,
  36         word             * so )         /* [0..159]     IN/OUT  */
  37 {
  38
  39         word       z1 = S->z1;
  40         longword L_z2 = S->L_z2;
  41         word       mp = S->mp;
  42
  43         word            s1;
  44         longword      L_s2;
  45
  46         longword      L_temp;
  47
  48         word            msp, lsp;
  49         word            SO;
  50
  51         longword        ltmp;           /* for   ADD */
  52         ulongword       utmp;           /* for L_ADD */
  53
  54         register int            k = 160;
  55
  56         while (k--) {
  57
  58         /*  4.2.1   Downscaling of the input signal
  59          */
  60                 SO = SASR( *s, 3 ) << 2;
  61                 s++;
  62
  63                 assert (SO >= -0x4000); /* downscaled by     */
  64                 assert (SO <=  0x3FFC); /* previous routine. */
  65
  66
  67         /*  4.2.2   Offset compensation
  68          *
  69          *  This part implements a high-pass filter and requires extended
  70          *  arithmetic precision for the recursive part of this filter.
  71          *  The input of this procedure is the array so[0...159] and the
  72          *  output the array sof[ 0...159 ].
  73          */
  74                 /*   Compute the non-recursive part
  75                  */
  76
  77                 s1 = SO - z1;                   /* s1 = gsm_sub( *so, z1 ); */
  78                 z1 = SO;
  79
  80                 assert(s1 != MIN_WORD);
  81
  82                 /*   Compute the recursive part
  83                  */
  84                 L_s2 = s1;
  85                 L_s2 <<= 15;
  86
  87                 /*   Execution of a 31 bv 16 bits multiplication
  88                  */
  89
  90                 msp = SASR( L_z2, 15 );
  91                 lsp = L_z2-((longword)msp<<15); /* gsm_L_sub(L_z2,(msp<<15)); */
  92
  93                 L_s2  += GSM_MULT_R( lsp, 32735 );
  94                 L_temp = (longword)msp * 32735; /* GSM_L_MULT(msp,32735) >> 1;*/
  95                 L_z2   = GSM_L_ADD( L_temp, L_s2 );
  96
  97                 /*    Compute sof[k] with rounding
  98                  */
  99                 L_temp = GSM_L_ADD( L_z2, 16384 );
 100
 101         /*   4.2.3  Preemphasis
 102          */
 103
 104                 msp   = GSM_MULT_R( mp, -28180 );
 105                 mp    = SASR( L_temp, 15 );
 106                 *so++ = GSM_ADD( mp, msp );
 107         }
 108
 109         S->z1   = z1;
 110         S->L_z2 = L_z2;
 111         S->mp   = mp;
 112 }